Adjust font size and color of email list (inbox; Posteingang) and message header in Thunderbird 68

userChrome.css

/* Thunderbird 68 has changed its architecture.
Unfortunately, many great themes and plugins are not working anymore.
The font size of the message list, where the emails of your inbox is listed, is way too small.
The standard and dark mode is a bit too dark.
You can easily fix that:

1. Search for your profile.
-> In Linux, you will find that unter  ~[home]/.thunderbird/<Profile name - usually quite cryptical>/
-> In Windows: C:\Users\<Windows user name>\AppData\Roaming\Thunderbird\Profiles\<Profile name>\

2. Go to the folder and create a new folder with the following name: chrome

3. Copy the file userChrome.css into this folder (chrome)

4. Restart Thunderbird 68 - that's it

---
What this small files will fix/change:

1. Font size of the listed emails in your inbox will be increased.
2. Unread messages are listed in warm orange
3. The buttons in the message header will also be in warm orange (background)
4. The message header - where you have the main information: from, subject, etc - is also displayed in a bigger font

*/

/* Change font-size of email list */
.tree-rows {
    font-size: 12px !important;
}

/* Set Line Spacing In Thread Pane */

#threadTree > treechildren::-moz-tree-row {

height: 24px !important; }

#threadTree treechildren::-moz-tree-cell-text(unread) {

color: #d78a57 !important;

font-size: 13px !important; }


/* :::::::::::: Message Header :::::::::::: */

/* This sets the background and text color of the buttons in Thunderbird 68 */

#header-view-toolbox {

background : #d78a57 !important; -moz-appearance: none !important;
font-size: 9pt !important;
color: black;
margin-bottom: 15px;
margin-top: 10px;
margin-right: 10px;
padding-bottom: 3px;}


/* This sets the font-size of the text in the message header */
#msgHeaderView {font-size: 11pt !important; }

/* This sets makes the subject line appearing bold */
#expandedsubjectBox .headerValue,
#collapsedsubjectValue{
font-weight:bold !important;}


/* Farbeinstellung im Dark-Mode */
/* Make Folders containing UNREAD messages visually distinct from others */
#folderTree > treechildren::-moz-tree-cell-text(folderNameCol, hasUnreadMessages-true) {
color: #FFA500 !important;
}

/* Change the appearance of folders which have a subfolder containing UNREAD messages */
#folderTree >treechildren::-moz-tree-cell-text(folderNameCol, subfoldersHaveUnreadMessages-true) {
color: #FFA500 !important;
}

/* Folder color when NEW messages arrive */
#folderTree > treechildren::-moz-tree-cell-text(folderNameCol, newMessages-true) {
color: #ff857c !important;
}


/* Highlight list items with a blue border and don't change background color */
treechildren::-moz-tree-cell-text(selected) {
color: #82bed8 !important;}

Wondering if you have been updating to the latest version 91.x.x? I put this as directed but will not load.. and can not see it as an addin.. Thoughts?

It should work, however, starting from version 78, you need to adjust a setting in the config editor. Otherwise, userchrome.css won't be read:

toolkit.legacyUserProfileCustomizations.stylesheets

Set this value to TRUE

Thanks for making this available to all. I just installed it following your instructions, it's absolutely perfect, I love being able to change colors/font size, boldness of incoming messages. Awesome!